GB1559577A

GB1559577A - Method of checking coins and coin checking apparatus for the aforesaid method

Info

Publication number: GB1559577A
Application number: GB4211276A
Authority: GB
Original assignee: LIBANDOR TRADING CORP Inc
Current assignee: LIBANDOR TRADING CORP Inc
Priority date: 1975-10-17
Filing date: 1976-10-11
Publication date: 1980-01-23
Also published as: FR2328251A1; JPS5250295A; IT1072865B

Description

(54) METHOD OF CHECKING COINS AND COIN CHECKING APPARATUS FOR THE PERFORMANCE OF THE AFORESAID METHOD (71) We, LIBANDOR TRADING CORPO RA rlox c., a Body Corporate organized under the laws of the Republic of Libera, of 80 Broad Street, Monrovia, Republic of Liberia, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement :- The present invention relates to a method of checking coins and to a coin checking apparatus for the performance of the aforesaid method.

A heretofore known method of checking coins contempiates conducting the coins to be checked in succession through the alternating-current fields of two successively arranged oscillator coils dimensioned such that at the first oscillator coil, when in Huenced by a"proper"coin, the oscillations of the oscillator just begin to breakdown and at the second oscillator coil the oscillations do not quite breakdown. The different dimensions of both oscillator coils govern the permissible stray range for a certain type of coin. Only when, as described, the one oscillator stops and the second does not, is the coin accepted.

While this technique can be put into practice econcmical ! y, still it is qualitatively unusable. The criterion"stopping of the oscillations of the oscillator", of all conceivable criteria, is the one which is most temperature-dependent, and even with constant environmental conditions is not accu- ratelv reproducable.

According to a further prior art process for checking coins there is employed a bridge-measurement circuit This technique has become known in numerous modifications. While it has the advantage of extreme accuracy, it is associated with the drawback that it is difficult to fabricate and has relatively high manufacturing costs and equally is not suitable for use as a multiple-coin checking device. It is characterized by a bridge which in one of its branches is pre-loaded either by an original coin or an appropriate electrical magnitude and the other branch is loaded by the coin to be checked. What is evaluated is the one-time self-adjustment of the nulI voltage, which only can be obtained if the strictly predetermined original coin is compared with an equivalent coin.

Further state-of-the-art methods utilize the damping of a transformer by means of a coin moving therepast which is to be checked, and owing to the influence of the coin there is reduced the HF-no loadamplitude at the secondary coil. The degree of damping, i. e. the maximum amplitude of a negative measurement voltage at the secondary, is used as the criterion for the recognition of a coin type.

Another group of already known coin checking methods employ the evaluation of positive measurement voltage amplitudes at the secondary coil, as such occur during de-tuning of symmetrically constructed differential-transformer probes.

Both the evaluation of the maximum damping at the secondary coil as well as the evaluation of the maximum nonsymmetry at the secondary coil result in good recognition of the different coin types.

But both techniques are associated with the drawback that they require complicated circuit design to obtain good Temperature stability. In any event both of the lastmentioned methods enable, by means of a single measurement arrangement, the recognition of different types of coins, since it is only necessary to utilize a corresponding number of window circuits in order to monitor the measurement voltage regions corresponding to the individual coin types to be checked. However, with both methods the circuits required are critial and expen- sive to manufacture.

According to one aspect of the invention, there is provided a method of checking a coin or coins comprising passing the coin or coins through an alternating electromagnetic field of a measuring coil energised by an alternating signal, comparing the amplitude of the alternating signal with a reference signal to produce a correction signal whose level is dependent on the difference between the alternating signal and the reference signal, controlling the amplitude of the alternating signal with the correction signal so as to maintain the said amplitude substantially constant, determining whether the level of the correction signal is between upper and lower limits which define a range of levels produced by accepatble coins, and selecting a time constant of the correction signal so as to be fast enough not to regulate on half cycles of the alternating signal but so as to be slow enough to allow as much of a variation of the amplitude of the alternating signal as possible as a result of passage of the coin or coins.

According to another aspect of the invention, there is provided an apparatus for nerforming the method according to the invention, comprising an oscillator connected to or mcluding a measured coil for producing a field through which the coin or coins to be checked can be passed and arranged to energise the coil with an alternating signal a comparator circuit arranged to compare the amplitude of the alternating signal with a reference signal and to supply to the oscillator from its output a correction signal for maintaining the amplitude of the alternating signal substantially constant, and an evaluation circuit connected to the comparator circuit output and arranged to produce a signal dependent of whether the level of the correction signal is between upper and lower limits which define a range of levels produced by acceptable coins, there being arranged between the oscillator and the comparator a time constant which is fast enough not to regulate on half cycles of the alternating signal but slow enough to allow as much of a variation in amplitude of the alternating voltage as possible as a result of passage of the coin or coins.

The invention will be described by way of examples with reference to the accompanving drawings, wherein :- Figure 1 schematically illustrates a first exemplary embodiment of a coin checking apparatus of the invention : Figure IA illustrates a circuit diagram of the logic circuit used in the arrangement of Figure ! : Figure 2 schematicallv illustrates a second exemplary embodiment of coin checking apparatus according to the invention; Figure 2A illustrates details of the logic circuit used in the arrangement of Figure 2; Figure 3 illustrates a third exemplary embodiment of the electrical circuitry of a coin checking apparatus of the invention ; Figure 3A illustrates details of the logic circuit used in the arrangement of Figure 3; Figure 4 is an electrical circuit diagram of a fourth exemplary embodiment of the coin checking apparatus of the invention; Figure 5 is an electrical circuit diagram of a fifth exemplary embodiment of a coin checking apparatus of the invention; Figure 6 illustrates a circuit diagram of a galvanicaily coupled coil as the measuring coil ; Figure 7 is a circuit diagram illustrating a transformer-coupled coil as the measuring coil ; Figure 8 illustrates a circuit diagram of a transformer-coupled pair of coils of a differential transformer serving as the measuring coil ; Figure 9 is an exemplary embodiment of the construction of a coin channel of a coin checking apparatus; and Figure 10 is a further exemplary embodiment of the construction of a coin channel of a coin checking apparatus.

Referring to Figure 1, an oscillator 12 having a measuring coil 11 as the oscillator coi ! : s operated via an influencing element 14 (for instance a voltage divider which can be controlled at its center tap and a regulatable resistor), such that there is produced in the measuring coil 11 a given oscillator voltage U, at a predetermined frequency F, which is tapped-off and rectified in a rectifier 16. This rectified no-load or idling measuring voltage Un and a reference voltage Ur,, (from a source 17) are delivered to a differential amplifier 18 which, bv means of the influencing element 14 located at the input of the oscillating circuit 12, stabilizes or controls deviations of the volt aè'. N for such length of time until Uc and Un.-r again coincide. The differential amplifier thus compensates all temperature-or other long duration effects upon the voltage UX or U, ; respectively, whether of an electrical nature (component drift) or mechanical nature (expansion and so forth).

Tn order to further prevent these variations, the differential amplifier also will control or regulate-out the amplitude of a sinusoidal oscillation of the oscillator bv having an appropriately dimensioned timeconstant which for this purpose functions as the regulation delay.

The regulation voltage U, ; resuming from the temperature-and long-time influences which are to be controlled or stabilized is extremely small and approximately equal to null during idling or no-load, since such influences slowly slip away. The no-load condition of the proposed measuring circuit is thus characterized by a constant maintained voltage Uf, of a certain magnitude and a regulation voltage UR of a certain amount (in the ideal case equal to zero) and thus UG=UXe- Experience has shown that coins in a given cairn checking apparatus always pass the measuring arrangement with an approximately defined velocity independently of whether they roll, slide or drop. As a function of the selected mechanical construction the speed of movement of the coins thus is defined within a certain region and this given speed of movement of coins must be taken into account for the selection of the time-constant of the differential amplifier and the timing element of the feedback loop as well as the operating frequency.

If, for instance, a coin drops through the field of the coil of the oscillator circuit, then the influence upon the oscillator circuit, brought about by the coin, is immediately counter-regulated via the differential amplifier, so that the voltage U, present at the measuring coil cannot decrease. Corresponding to the influence of the coin there thus is formed, as the regulation magnitude, a regulation voltage for compensating such influence, which is tapped-off and, as proposed, can be used directly as the new criterion for the coin measurement because its value is proportional to the effect of the coin upon the oscillator circuit and is available as a positive rectified signal voltage. As will be apparent from the discussion of the following exemplary embodiments it is possible to realize, with the proposed method, simple, inexpensive and especially nonsensitive and temperature-stable measurement arrangements for checking coins.

As the regulation magnitude for the criterion for checking of the coins there can be employed, for instance, the regulation voltage or regulation current. The examples discussed hereinafter relate to the evaluation of a regulation voltage. However, it is here mentioned that of course it would be equally possible to evaluate the regulation current.

With a single measuring coil it is possible to check a number of different types of coins. But in those instances where the required checking accuracy is not adequate, it is possible to also use two or more oscillator circuits and to check each coin in succession in the different oscillator circuits. The individual oscillator circuits advantageously operate at different frequencies and thus provide different information regarding a certain type of coin.

In those cases where there are employed for checking the coins two or more coils for oscillating circuits operating at the same frequency, the oscillating circuits are advantageously slightly detuned relative to one another in order, in this manner, to eliminate any mutual influence upon one another.

It is immaterial whether the oscillator is operated predominantly unstable and the regulated magnitude (voltage or current) is exclusively assigned the function of maintaining constant the oscillator-measuring voltage of the measuring coil (or, better, the rectified oscillator-measuring voltage at the input of the differential amplifier) or whether the frequency and voltage are stabilized and the current regulated, or only the voltage stabilized and the current regulated. or only the current stabilized and the voltage regulated. These different possibilitics are available ; the choice may be left to the circuit designer in consideration of the component expenditure.

The proper selection of the suitable timeconstant for the regulation circuit is decisive.

This must be tuned to the throughpass time of the coins to be checked and the selected operating frequency. The throughpass time is governed by the construction and must be determined by measurements. What is attempted to be attained when selecting the time-constant is that the regulation should be calcuIated to be rapid enough that it can still immediately counter-regulate the influence of the coins moving quickest through the measuring coil or winding, in other words there does not occur any appreciable change in the amplitude of the noload oscillator-measuring voltage at the measuring coil, but, on the other hand, not so rapidly that it, as already mentioned, controls or stabilizes the half waves of the alternating oscillator-measuring voltage at the inverting input of the differential amplifier.

In contrast to all other already known quasi-static functioning methods the methods here proposed are quasi-dynamic and functions only in conjunction with a defined speed of movement of the coins and a defined time-constant of the regulation circuit which is tuned thereto.

Stationary, too slow moving or too rapidly moving coins, that is to say, coins which move outside of a certain velocity tolerance band, do not produce any evaluatable amplitude (too small or distorted) of the regulation magnitude to be measured.

Further, it is advantageous if the circuit arrangement is constructed such that the circuit components of the differential amplifier bring about a separation of the "long-time regulation magnitude"from the"coin-regulation magnitude", and in the embodiments described hereinafter examples will be given.

It is further advantageous if an additional voltage divider between the timing element determining the time-constant and the input of the regulatable resistor steps-down the regulation magnitude, and thus, brings about that the amplitude of the regulation magnitude at the output of the differential amplifier is correspondingly greater and hence also the amplitude of the regulation magnitude which is employed for the coin checking.

The travelling-or slide track upon which move the coins to be checked can be provided at a small spacing from the throughpassing coins, with one or a number of measuring coils of one or a number of oscillation circuits, so that the coins can pass witll their edges facing the measuring coil or coils. With the particular advantage of increased recognition accuracy it is also possible to enclose the coin chute or channel intended for guiding the coins with one or a number of narrow ring-like measuring coils.

With the coin checking apparatus illus- trated in Figure 1, a coin 1 to be checked is permitted to free fall through a chute or channel 4 formed by side walls 2 and 3.

In the event that the coin 1 is not accepted it is conducted by means of a classification or sorting chute 5 into a return chute 9 formed by side walls 6 and 7. In the event of coin acceptance the classification or sorting chute 5 is rocked about a shaft 51 and thereby conducts the coin I into an aeceptance ehute 10 formed by side walls 7 and 8.

The classification or sorting chute 5 is retained in a rest position by a spring 52 against a stop 53. It is operable by an actuation magnet 50 such that when the latter is energized it causes pivotal or rocking movement of the classification chute 5 over the acceptance chute 10.

Arranged around the drop chute or channel 4 is the coil or winding 11 of an oscillating circuit consisting of the winding or coil 11 and a frequency-determining element 13 e. g. a capacitor. The control of the oscillator 12 occurs by means of the influencing element 14 for instance a regulaiable or variable resistor. Reference character 15 designates a feedback loop or line for a stabilization, and reference character 151 a feedback resistor.

In ihe idling or no-load state there should appear at the coil 11 an oscillatormeasuring voltage of a certain value (nvolts), which is tapped-off and rectified in rectifier 16. The rectified no-load voltage (IJ, ;) is delivered to the differential amplifier 18, for instance the commercially available "type 741"of Motorola Company, or another suitable amplifier. The second input of the differential amplifier 18 has supplied thereto a reference voltage of n volts produced by the reference voltage source 17. In the rest state there is valid the relationship U,,, =UG. Upon passage of the coin through the measuring coil there is valid, slightly time-delayed owing to the regulation or readjustment. likewise the re lationship Unef=Uu.

The regulation circuit is connected via a line or conductor 181 to the regulatable resistor 14. There appears at the conductor or line 181 a regulation voltage when the predetermined oscillator no-load voltage appearing at the measuring coil 11 changes.

Since, however, the temperature-or longtime eftects, which should be controlled or stabilized in this manner, only appear in a creeping or slow manner, in the normal instance this regulation voltage, that is to say, when no coin is dropping through the measuring coil li, remains very small and almost equal to null. The time-constant of the regulation circuit is thus determined by the RC-element composed of the resistor 182 and the capacitor 183.

From the circuit arrangement it will be apparent that owing to the continuous stabilization of all conceivable effects upon the oscillator circuit there can be employed very simple and inexpensive components, without losing the desired high temperaturestability. The small number of inexpensive components and the elimination of any tuning work constitute economies of the proposed method.

Now if the coin I drops through the field of the measuring coil 11 with an approximately determinable speed which is taken into account during calculation of the time-constant of the regulation circuit, then at the output of the differential amplifier i8 there appears at the line 181 a regulation voltage. This regulation voltage becomes that much greater, the greater the influence of the coin 1 upon the alternatingcurrent field of the measuring coil 11. This regulation voltage is directly proportional to the change of the field by the coin, since it compensates such and maintains constant the predetermined voltage at the measuring coil 11.

Tt has already been mentioned that the time-constant of the regulation circuit can be dimensioned to be appropriatelv large mhile taking into account the stabilization or control of the oscillator oscillations. On the other hand, it must however be chosen, as a function of the operating frequency and the speed of movement of the coin, to at least be so small that there can occur in any event a counter-regulation. Starting from these boundary magnitudes the time constant must be optimized such that a predetermined maximum influence of the oscillator coil corresponds to a maximum possible proportional regulation magnitude.

For example, with coins dropping in a certain given coin checking construction, it may happen that it can be approximately assumed that such move through a distance of 2 j 10 mm (one fifth of a millimetre) per millisecond. This distance may correspond approximately to the path which is critical for the determination of the maximum influence. i. e. a coin in this example has its maximum influence upon the magnetic fielol of the oscillator coil at a certain location and still has an influence throughout a distance range of about 1/10 mm in both directions, which approximately corresponds to the absolute maximum. At greater spacing of the coin in each of both directions from its ideal position (i. e. the position where there is brought about the absolute maximum of the influencing effect) the influencing action decreases markedly and becomes increasingly intolerable for carrying out coin checking. The actual measuring operation for a coin located in the mentioned construction thus occurs over a distance of approximately 2/10 mm and within a time period of about 1 millisecond.

While observing the selected operating frequency of the oscillator coil the time constant can be chosen to be so small that the regulation circuit is capable of controlling or stabilizing changes resulting upon passage of the coin through the coil, so that no appreciable change of the amplitude of the HF-no-load voltage at the measuring coil 11 occurs during the fallthrough of a coin. As a result, for measuring a dropping coin there must be furthermore chosen a certain minimum frequency if it is to be avoided, to advantage, that the sinusoidal oscillations of the oscillator will be regulated-out or stabilized (some tlling which should not occur).

It is therefore apparent that the proposed method for mcasuring coins does not operate quasi-statically, rather quasidynamically and with the aid of an appropriate time-constant: It is thus possible to designate the method as a quasidynamic method. It further will be seen that for appropriate dimensioning of the oscillating circuit and the regulation circuit there must be present the approximate speed of movement of the coin, since a time-constant which has been optimum chosen in consideration of a pronounced regulation magnitude and therefore as good as possible detection of the coin. With the case of a coin which moves too slowly (for instance a coin lowered on a thread into the coin checking device) it does not deliver any or only a slightly falsified and weakened signal information. In this way there is achieved the beneficial result that the propcsed method for checking coins, in consideration of the security against being deceived by thread tricks, is far superior to all other heretofore known methods, all of which operate statically.

The previously mentioned minimum frequency which must be present at a given speed of movement X of the coins, is lower in the case of a traveling or rolling coin than in the case of a very rapidly moving coin (free fall or rapid mechanical con veying).* The already mentioned regulation voltage is tapped-off by conductor 19 and delivered to an evaluation circuit comprising a window circuit 20 consisting of a lower voltage threshold 21 and an upper voltage threshold 22, which may be as shown, operational amplifiers, but also could be constituted by diodes or transistors. The outputs of both voltage thresholds are connected with an exclusive-OR gate 23, which upon response of only one threshold delivers an output signa'and does not deliver any output signal when no voltage threshold is excited or both voltage thresholds are excited. Thus, if the amplitude to be detected of the regulation voltage does not reach the predetermined window range or region, then the subsequently connected logic circuit 24 does not receive any pulse.

If the maximum value of the regulation voltage enters the window region, then the logic circuit 24 receives a pulse. If the window region is exceeded at the upper boundary, then the logic circuit 24 receives shortly in succession two pulses: one upon ascent of the regulation voltage into the window region and until leaving the window region at tle top, a further pulse upon again entering from above the window region and until leaving the window region at the bottom.

The logic circuit 24 is designed such that upon occurrence of a first pulse a timing device or stage 241 suppress for a certain time the evaluation of the stored signal or signals and after expiration of such time determines whether there has arrived at a counter 240 one signal or two signas. Only the output I of the counter 240 is connected with the output of the timing stage 241 via a gate, sa that its output signal can be evaluated by means of the output lines 25j26, for instance for counting the coins.

The duration of this output pulse upon the line 25 is determined by the timing element 242, the time of which is greater than that of the timing element or stage 241. The difference of both times determines the duration of the output signal, because the timing element 242 accomplishes by means of the descending flank or slope of its timing signal extinguished of the counter 240.

By means of the lines 25/27 the output signal is delivered to a driver stage 28 which controls the magnet 50. In the described exemplary embodiment the control times for the magnet 50 an dan external counter 29 are the same. If necessary, there can be realized in conventional manner also a different control time for the magnet 50 and the counter 29 in that, for instance, a further counting stage is incorpo- rated into one of both signal lines 26 or 27. The positively directed regulation voltage which has been described on the basis of the showing of Figure I and employed for evaluation, is for certain coins very small, because also the influence upon the oscillation circuit bv the coin, due to its smaller dimensions and its material, in many cases, is only very small. A very small voltage, however, is dimcuit to detect for reasons of circuit design.

For instance, a very small coin generates, during falling through the measuring coil, a regulation voltage of 50 2 mV so that the spacing between the upper and lower thresholds of a window circuit monitoring the regulation voltage amounts to 4 mV.

It should be clear that nothing can be eSectively accomplished with such low signal levels if the evaluation circuit is designed with acceptable low component expenditure.

Hence, it is very desirable to obtain, even when the oscillation circuit is slightly influence by a coin, increased evaluatable amplitudes through the provision of additional measures, so that it is possible to employ simpler and less expensive evaluation circuitry. Two possibilities are obtaining an increased sensitivity of the oscillating circuit and therefore a correspondingly greater regulation voltage and/or obtaining greater regulation magnitude at the output of the differential amplifier which is greater than the direct proportional relationship for damping of the oscillating circuit.

Therefore, it is preferred to operate the oscillating circuit at resonance (resonance frequency) in order to make use of the coherent resonance step-up which comes into play due to the measuring coil during throughpassage of a coin.

Tt is also nreferred to supply the positive amplitude of the regulation voltage, result- ing from the innuence upon the measuring coil tuned to resonance or another random freouency, to the inclut of the regulator oscillator by means of a voltage divider of a certain ratio so that for thX purpose oE obtainmg a sumcient regulation magnitude at the input of the regulatable oscillator. by means of the differential amplifier in the regulation circuit there i 181 which steps-down the regulation voltage in a certain ratio and thus requires that there must be delivered a correspondingly greater voltage by the differential amplifier 18 if there is to be obtained the voltage neede (l lor the regulation at the output of the regulatable resistor 14.

As stated with regard to the discussion of Figure I, the regulation magnitude generated by the coin should be measured and which magnitude is directly proportional to the influence of the oscillation circuitamplitude by the coin. When in toto there are present stable conditions in the circuit and not too great a temperature range, then the circuit of Figure 1 or 2 can be employed, because, in the normal instance, the regulation magnitude almost exclusively expresses the influence upon the oscillation circuitamplitude by the coin, and the proportion, which continually is present for stabilizing the drift or the like, is so small that the coin measurement does not appreciably suffer in accuracy. This, however, requires care in selecting the time-constants. Such can, however, cause difficulties if the speed of movement of the coins varies slightly.

Also, in those instances where there are employed extremely inexpensive components for the purpose of reducing fabrication costs and all temperature stabilization ex penditurz is avoided or where there is taken into account a large temperature range, then the circuitry of Figures 1 or 2 can become much too inaccurate, because that portion of the regulation magnitude which serves for stabilization or controlling the longtime influences reaches a considerable portion, and accordingly, increasingly reduces the accuracy of the coin measurement. With appropriate circuit design of the differential amplifier 18 it is, however, possible to achieve the result that the re gulation magnitude, brought about by the coin and corresponding to its influence upon the oscillating circuit, can be measured independently of that regulation magnitude which might prevail with an undetermined magnitude for stabilizing slow-type appearing or creeping influences. The subsequently described circuits of Figures 3,4 and 5 thus relate to exemplary embodiments which disclose how it is possible to more advantageously design the circuitry of the regulation circuit 180. Further modifications can be realized according to known principes of circuit design. In Figures 4 and 5 certain of the components, corres ponding to those of Figures 1 to 3. have been designated by the same reference character followed by the digit"0".

The separation of the"coin-regulation magnitude"from the"long-time regulation magnitude"is thereby possible if there is utilized their different time behaviour; long-time or long duration influences appear slowly, the coin-influences appear relatively rapidly as already previously described.

It is possible to proceed in two different way s : (a) There can be employed a circuit which stabilizes or controls the long-time regulation magnitudes which appear slowly, so that the rapidly appearing coin-regulation magnitudes always can be measured from (approximately) null (Figure 4).

(b) There can be used a circuit which cannot detect slow appearing long-time regulation magnitudes, but however detects the rapid appearing coin-regulation magnitudes (Figures 3 and 5).

The solution of the first circuit function (Figure 4) consists of, for ; nstance, providing an additional coupling from the output of the differential amplifier 18 to one of its inputs via a null value-comparator circuit connected as an integrator. This comparator insures that the output regulation magnitude of the differential amplifier 18 is fedback or positively fedback at one of its two inputs and thus there is eliminated the voltage difference at both inputs.

Which input of the differential amplifier is connected to the integrator depends upon the polarity of the integrator-output voltage: with negative output voltage of the integrator the reference voltage is artificially lowered (this possibility is illustrated in Figure 4), with positive output voltage of the integrator the measurement voltage is artificially increased. Tn both instances the output regulation magnitude of the differential amplifier 18 becomes null.

The solution of the second circuit function (Figures 3 or 5) consists of, for instance. in either a"-dynamic forward loop or coupling"from the measuring voltage input of the differential amplifier 18 to its output (Figure 5) or, for instance, in a"dynamic feedback loop or coupling"from the output of the differential amplifier 18 to the input of the influencing element 14 at the input of the oscillator circuit (Figure 3). In contrast to known forward coupling circuits the"dynamic forward coupling-circuit" disclosed in Figure 5 advantageously consists of a diode 185, a capacitor 184 and a resistor 186 connected in series. The diode 185 during low peaks blocks the current flow from the measuring voltage input of the differential amplifier 18 to the capacitor 184 and the resistor 186 serves as a charging-and discharging-resistor for the capacitor 184 to the output of the differen tial amplifier 18 and also determines the time-constant.

What is common to the embodiments of Figures 4 and 5 is that the time-constant for the feedback or the forward coupling at the differential amplifier input is greater than the time-constant for the feedback at the influencing element 140 (or 14) at the input of the oscillator circuit.

In contrast to the feedback circuitry described in Figure 1, the"dynamic"feedback circuit illustrated in Figure 3 is constituted by a capacitor 33 and a diode 31 connected in series, and in parallel thereto a resistor 32. Advantageously, the capacitor 33 is connected with the output of the differential amplifier 18 and thus, the diode 31 is poled towards the input of the oscillator 12. The remaining reference characters designate components corres ponding to those of Figure 1.

Moreover. the embodiment of Figure 3 has the advantage that calculation of the time-constants for the"dynamic"feedback is considerably less critical than that of the time-constants for the feedback according to Figure 1.

Thus, it is possible to define the described improvements also as"regulation circuit with two feedback couplings or loops" (Figure 4) or"regulation circuit with a feedback coupling or loop and a forward coupling or loop" (Figure 5) or"regula tion circuit with a dynamic feedback loop or coupling" (Figure 3). The mode of operation of the three examples of circuit connecting the differential amplifier 18 will be described hereinafter.

At this point it is mentioned that the operating point of the of the amplifying transistor e. g. the transister 121 (see Figures 4 and 6) of the oscillator 12 is located along g the steep portion of the resonance curve in order to obtain increased sensitivity of the oscillating circuit when influence by a coin, and thus us to obtain increased recognition accuracy.

Aiso m this case there is formed a regu lation magnitude from the difference of the reference voltage and the rectified measure ment or measuring voltage at the input of the differential amplifier 18, which regula tion magnitude, in the ideal case, during no load, is equal to null.

With slow changes of the coincident of U, ;,, ; and U, ; due to drift or the like, there arises a modifie no-load regulation magnitude of certain and low magnitude which readjusts the oscillator by means of the re sistor 32, the voitage divider 189 and the influencing element 14. Since the diode 31 blocks, the capacitor 33 cannot charge with slow and slight changes of the regulation magnitude. An approximately continuously prevailina long-time regulation magnitude thus does not reach the capacitor and the tap for the measuring voltage for the coin evaluation.

In the case of more rapid and pronounced changes of the regulation magnitude, such as upon passage of a coin through the measuring coil 11, there appears at the output of the differential amplifier 18, also at the input of the dynamic feedback circuit 30, a greater voltage than at the output of the dynamic feedback circuit. Since the diode 31 functions as a pole-dependent current valve, the capacitor 33 can suddenly charge. Its charging voltage corresponds to the increase of the regulation magnitude, which has been brought about by the coin, and therefore can be tapped-off as the measurement magnitude between the capacitor 33 and the diode 31 for the evaluation of the coin In contrast to the circuitry of Figure 1 the circuitry of Figure 3 has the further advantage that it is more suitable for mass production. As already mentioned, the dimensioning of the optimum time-constants for the circuit of Figure 1 is critical and therefore in this case there must be employed components (resistor and capacitor) which have been fabricated within narrow tolerances or must be tuned thereto. Owing to the separation of the long-time regulation magnitude from the coin-regulation magnitude, due to the blocking action of the diode as above described, the dimensioning of the optimum time-constants for the dynamic feedback is less critical, and can be realized without tuning with normal, i. e. inexpensive components.

Due to the separation of the long-time regulation magnitudes and the coinregulation magnitudes it is further possible, in contrast to the example of Figure 1, also to dispense with tuning of the reference voltage or the HF-measuring voltage. In Figure 1 it was necessary to have exactly in coincidence the reference voltage and the rectified measuring voltage, in order to obtain for no-load a regulation magnitude of null, and thus, to achieve as small as possible long-time regulation magnitude for stabilizing possible drifts. With the embodiment of Figure 3 it is sufficient if the reference voltage is not less than the recti- fied measuring voltage. This can be however, easily achieved with standard components if the reference voltage is calculated to be slightly larger than the.rectified oscillation-measuring voltage. This indeed does result in the differential amplifier 18 continually producing a regulation magnitude of certain value already under noload condition. Since, however, with the embodiment of Figure 3 the long-time regulation magnitude does not have any disturbing effect within a certain range, this does not have any influence upon the accuracy of the coin measurement, rather only brings the considerable advantage of eliminating anv type of tuning work.

It was stated in the preceding description of Figure 1 that in the ideal case the idling control quantity equals zero and must be zero.

If the circuit is so constructed that a separation of the"long-term control quantity"from the"coin-control quantity" occurs, this demand does not apply any more.

Therefore in the example according to Figure 3 the differential amplifier (18) may be operated with only one (positive) supply voltage. Caused by its construction, in this case the control of a differential amplifier docs not begin until a certain voltage difference prevails at its'inputs, because the"minimum voltage at the output"has a certain amount (e. g. 2,5 volts) when the differential amplifier is operated with only one supply voltage. The reference voltage may be selected without difficulty so much higher than the non-regulated rectified oscillator measuring voltage that the differential amplifier, in the idling case, must continuously supply a certain control quantity (for example 4.0 volts) in order to maintain UG and URe, in agreement.

A difference between the idling control quantity (for example 4 volts) and the "minimum voltage at the output" (for example 2. 5 volts) of (for example 1.5 volts) means that the differential amplifier has free movement to the low voltage side, too.

The"dynamic feedback"has the effect that even such a relatively high idling control quantity does not lead to charging the capacitor 33 and is not measurable by the evaluation circuit 20).

Ou ! y a rapid (dynamic) voltage rise be yond the (static) idling level is detected.

Thus in this case only the control quantity is evaluated which is generated by a coin during its passage through the alternating current field of an oscillator measuring coil, namely in this case the difference between a long-term prevailing static idling control quantity and a voltage maximum which is produced suddenly in consequence of the influence of the travelling coin.

The same advantage of simpler and less expensive fabrication for mass production without any tuning work exists with the circuit embodiments of Figures 4 and 5, wherein such advantages however are merely achieved in a different manner as will be explained hereinafter.

In Figure 4 there are again disclosed the individual function blocks appearing in Figure 1 and here described in greater detail.

The supply voltage is designated by reference character 100, the negative supply voltage by reference character 200, ground is designated by reference number 0. Reference character 120 designates the oscillator which corresponds to the components 11,12,13 and 151 of Figure 1. In the example of Figures 4 and 5 there is shown a conventional capacitive three-point oscillator, arranged in an emitter circuit configuration consisting of the transistor 121, the coil 122 and the capacitors 123,124 and 125. The capacitor 124 determines the oscillating frequency, the capacitor 125 serves for feedback, the capacitors 123 and 125, in conjunction with the resistors 126 and 127, determine the operating point which is centrally located. Owing to the foregoing the differential amplifier 18 can detect voltage deviations of the rectified oscillator measuring amplitude.

The control of the oscillator 120 (by varying the working point of transistor 121) occurs with a predetermined selected operating voltage by means of the influencing element 140 (consisting of the resistors 141. 142 and 182 and capacitor 183) by means of which the oscillator oscillates at a predetermined HF-amplitude. The operating voltage may be supplied by an attenuator (not shown). The thus obtained HF-voltage is rectified in the rectifier 16 consisting of the diodes 161 and 162, filtered by means of the filtering capacitor 163 and delivered to the inverting input of the differential amplifier 18. The reference voltage is obtained by means of the reference voltage source e. g. the voltage divider 17 consisting of the resistors 171 and 172. It is here again mentioned that all of the illustrated solutions are only intended as exemplary and are not in any way intended to limit the scope of the invention. For instance, instead of obtaining the reference voltage by means of a voltage divider from the supply voltage, this reference voltage of course also could be obtained from a fixed voltage source, such as the source 17 of Figure 1, or by means of a reference diode or in any other randomly selected manner.

The manner of obtaining the reference voltage as indicated by way of example from the supply voltage is always then possible if the operating point of the oscillator and the reference voltage are located in the same relationship, since only then is there realised an extensive non-dependency of the measuring accuracy from fluctuations of the supply voltage. The operating points should not shift.

Also, a free selection of the oscillator is possible as long as such delivers an output amplitude which is in a fixed relationship to the applied supply voltage. Thus, there could be equally employed, for instance, an oscillator designed as a Meissnercircuit or a Cholpitz-circuit, a quartz oscillator or any other suitable oscillator.

In order to preserve clarity in illustration the function blocks 20,23,24,28 and 29 of Figure 1, in other words the entire signal evaluation, have been illustrated in corresponding manner in Figure 4 simply as the function block 300, and the classification or sorting magnet has been indicated by reference character 50. Only the externai circuitry of the differential amplifier 18 for separately obtaining the coinregulation magnitude determined solely by the coins has been individually illustrated in Figures 4 and 5.

Both examples insure that the coin regulation magnitude, brought about by the action of the coins, is measured independently of any possibly prevailing long-time regulation magnitude. Other examples are possible while taking into account the described concepts of the invention, for instance by utilizing the base-emitter voltage of a transistor.

In Figure 4 the output regulation voltage of the differential amplifier 18 is delivered via the conductor or line 181 and a resistor 196 to the inverting input of a comparator 198, the other input of which is at ground potential. The comparator 198 continuously compares the infed positive output regulation voltage of the differential amplifier 18 with null and in turn delivers a negative regulation voltage. The latter is supplied to the non-inverting input of the differential amplifier 18 (equal to the reference voltage input) and thus terminates the non-coincidence of both input voltages. in other words eliminates the regulation or control of the differential amplifier 18.

In order to render perceivable the rapid changes of the regulation voltage during passage of a coin the comparator 198 must be designed as an integrator, and the timeconstant of the capacitor 197 and the resistor 196 chosen such that it is slower than that of the feedback coupling at the input of the oscillator via the influencing element 140.

The circuit thus operates in the manner that the output regulation voltage of the differential amplifier 18 through the integrator in the feedback loop at the input of the differential amplifier 18 is employed for correcting thc reference voltage with slow changes and is terminated by correction of the reference voltage. The longtime regulation magnitude is thus always led to the value null, so that in the case of a coin measurement the rapid changes of the regulation magnitude, brought about by the action of a coin, can be separately tapped-otT. The here described circuit fulfills the greatest requirements in accuracy and stability. The only drawback is the requirement for two supply voltages and two operational amplifiers 18 and 198.

Now in Figure 5 there is illustrated an embodiment of circuitry which can function with a single supply voltage and wherein the. circuitry of the differential amplifier 18 requires neither a further operational amplifier nor an additional transistor or the like.

The already mentioned dynamic forward coupling or loop contains a capacitor 184 which cannot charge with slow changes of the regulation voltage at the output of the differential amplifier 18, because the diode 185 blocks at the higher peak. If during the coin measurement the measuring voltage at the input of the differential amplifier 18 drops, then the regulation voltage at the output of the differential amplifier increases, and indeed considerably owing to the gain of the differential amplifier 18. Between both points there forms over the forward coupling line or loop a voltage gradient which leads to elimination of the blockinz of the diode, and thus, to a sudden charging of the capacitor 184 because the resistor 186, which for small peaks brings about a pronounced charging delay, now is no longer effective. The charging continues as ong as the voltage climbs and transforms into a discharge via the resistor 186 towards the output of the differential amplifier 18 when the voltage drop reduces.

Since these operations are determined by the speed of movement of the coins, the time-constant of the forward coupling is derived from the speed of movement of the coin, tuned to such and in any event slower than the time-constant of the feedback to the input of the oscillator via the influencing element 140. At the tap 187, better still at the tap 188 there can be tapped-off a dynamic signal, which only expresses those voltage increases which rapidly proceed, in other words emanate from a normally moving coin.

The influencing element designated bv reference character 140 in Figures 4 and 5 contains in conventional manner, by appropriate dimensioning, the components of the timing element for the feedback (182 and d 183 of Figure 1), the voltage divider (189 of Figure 3) and the influencing element designated by reference character 14 in Figure 1. In the same manner it could also be constructed such that instead of the timing element for the feedback loop it contains a timing element for the dynamic feedback In Figures 4 and 5, it being specificallv shown in Figure 4. the measuring coil 122 is a component of the oscillator 120.

In Figure 6 there is illustrated a circuit arrangement wherein the measuring coil 11 is salvanically courled with the oscillator 120 which, it will be seen, is constructed in the manner described above in conjunction with Figure 4 and therefore the same reference characters have been used for the same components.

In Figure 7 there is illustrated the transformer-coupling i. e. inductive coupling, of the measuring coil 11 with the coil 122 of oscillator 12, so that the coils 122 and 11 form a transformer.

In Figure 8 the out-of-phase, series connected coils or windings lla and llb form the measuring coil 11 which is transformercoupled with the coil 122 of an oscillator 12, and the coils 122 and 11 form a differential transformer.

In Figures 9 and 10 there is illustrated a coin checking apparatus denoted reference character 1000. its infeed funnel for the coins denoted by reference character 1001. and a drop channel situated therebelow and following the infeed funnel 1001 denoted by reference character 1002. A coin balance 1003 of known construction permits coins which are too small to fall down into the outlet 900 (coins which have not been accepted). Coins of the permissible diameter are laterally tilted away by the coin balance 1003 into a traveling chute or track 1004. Coins of too large diameter block and can be conveyed by an unlocking device, which is not illustrated, into the outlet 900.

In Figure 9 the travel path or track 1004 intended for the coins is inclined slightly laterally, so that a coin 1 can slide past, while in contact with a side wall of the traveling path or track 1004, and thus has a defined spacing from the coil 11, constructed as an end probe, of an oscillator circuit or equivalent means which, in turn, is connected with a coin checking circuit.

A classification or sorting flap 54 remains in rest position in the event of a false measuring result, so that the coin slides over the front side of the sorting flap 54 into the chute 910 which terminates at the chute 900 for non-accepted coins.

Tn the case of proper measurement results the magnet 50 of Figures 1 to 5, but not here shown to simplify the illustration moves the pivotal sorting flap 54 about its shaft 541, so that the coin can arrive at the chute 920 for accepted coins and which chute starts at the rear side of the sorting flap.

In Figure 10 the travel track 1004 for the coins is surrounded in a ring-like manner by a coil Il of an oscillating circuit, oscillator or equivalent means which, in turn, is connected with a coin checking circuit. A horizontally pivoting guide member 1005 remains in its rest position in the event of false measurement results, so that the coin can arrive in the chute 910 and from such into the chute 900 for nonaccepted coins. In the case of correct measurement results the magnet 50 of Figures 1 to 5 moves the horizontal pivotable guide member 1005 into the recess 1006 of the side wall to such an extent that the coin is hindered from dropping and can roll into the chute 920 for accepted coins begininng at the extension of the travel track 1004.

Hence, there can be realized multitypecoin checkers which have a coin balance 1003, a coin travel track 1004 with the coil 11 and a coin checking circuit, a magnet 50 with the sorting or classification element 54 or 55 respectively, and an acceptance chute for proper coins which merges with the travel track.

Claims

WHAT WE CLAIM IS :

1. A method of checking a coin or coins comprising passing the coin or coins through an alternating electromagnetic field of a measuring coil energised by an alternating signal, comparing the amplitude of the alternating signal with a reference signal to produce a correction signal with a reference signal to produce a correction signal whose level is dependent on the difference between the alternating signal and the references signal, controlling the amplitude of the alternating signal with the correction signal so as to maintain the said amplitude substantially constant, determining whether the level of the correction signal is between upper and lower limits which define a range of levels produced by acceptable coins, and selecting a time constant of the correction signal so as to be fast enough not to regulate on half cycles of the alternating signal as possible as a result of passage of the coin or coins.

2. A method as claimed in claim 1, in which the alternating signal is rectified and applied to one input of a differential amplifier, another input of which receives the reference signal, the differential amplifier providing the correction signal at its output.

3. A method as claimed in claim 1 or 2. in which the correction signal is provided with a time constant small enough to maintain substantially constant the amplitude of the alternating signals as a coin passes through the alternating electro- magnetic field but large enough to substantially eliminate from the correction signal components at the frequency of the alternating signal.

4. A method as claimed in any one of claims 1 to 3, in which the alternating signal is supplied by an oscillator including a transistor whose working point is controlled by the correction signal.

5. A method as claimed in claim 4, in which the control signal is supplied to the transistor via an attenuator.

6. A method of checking coins substantially as hereinbefore described with reference to the accompanying drawings.

7. An apparatus for performing the method of claim 1, comprising an oscillator connected to or including a measuring coil for producing a field through which the coin or coins to be checked can be passed and arranged to energise the coil with an alternating signal, a comparator arranged to compare the amplitude of the alternating signal with a reference signal and to supply to the oscillator from its output a correction signal for maintaining the amplitude of the alternating signal substantially constant, and an evaluation circuit connected to the comparator circuit output and arranged to produce a signal dependent on whether the level of the correction signal is between upper and lower limits which define a range of levels produced by acceptable coins, there being arranged between the oscillator and the comparator a time constant which is fast enough not to regulate on half cycles of the alternating signal but slow enough to allow as much of a variation in amplitude of the alternating voltage as possible as a result of passage of the coin or coins.

8. An apparatus as claimed in claim 7, in which the oscillator includes a transistor connected to the comparator circuit in such a way that the working point of the transistor is controlled by the correction signa !.

9. An apparatus as claimed in claim 8, in which the comparator comprises a differential amplifier having a first input connected i, ia a rectifier to an output of the oscillator and a second input connected to a reference signal generator.

10. An apparatus as claimed in any one of claims 7 to 9, in which the comparator circuit output is connected to the oscillator via a time constant circuit whose time con stant is smali enough to maintain substan tially constant the amplitude of the alternating signal when a coin passes through the field of the measuring coil but large enough to substantially eliminate from the correction signal components at the frequency of the alíernating signal.

11. An apparatus as claimed in any one of claims 7 to 10, in which the measuring coi ! is an oscillating coil of the oscillator.

12. An apparatus as claimed in any one of claims 7 to 10, in which the measuring coil is electrically connected to an oscillator coil of the oscillator.

13. An apparatus as claimed in any one of claims 7 to 10, in which the measuring coil is inductively coupled to an oscillator coil of the oscillator.

14. An apparatus as claimed in claim 13, ! n which, the measuring coil comprises two identical windings connected in series in antiphase.

15. An apparatus as claimed in any one of claims 7 to 14, in which at least one further oscillator and measuring coil is provided, the frequency of oscillation of each oscillator being different from that of each other oscillator.

16. An apparatus as claimed in any one of claim, 7 to 15, in which a or the time constant circuit connected between the comparator output and the oscillator comprises a resistor connected in parallel with a series circuit comprising a capacitor and a diode with one terminal of the diode connected to the oscillator, the evaluation circuit being connected to the junction of the diode and the capacitor so as to be connected to the comparator circuit via the capacitor.

17. An apparatus as claimed in any one of claims 7 to 15, in which the comparator circuit comprises a differential amplifier provided with a negative feedbck loop comprising a comparator which is connected as an integrator with its non-inverting input at ground potential and whose inverting input and output are connected to the output and an input respectively of the differential amplifier so as to maintain the inputs of the differential amplifier at the same time potential, the time constant of the mtegrator being large enough to sub stantially prevent an output signal of the integ : ato from changing when a coin passes through the field of the measuring coil, the evaluation circuit being connected to the differential amplifier output.

IS. An apparatus as claimed in any one of claims 7 to 15, in which the comparator circuit comprises a differential amplifier whose output is connected via a resistor to one terminal of a capacitor whose other terminal is connected via a diode to one of the inputs of the differential amplifier to form a negative feedback loop around the dilTerential amplifier, the evaluation circuit being connected to the junction between the capacitor and the diode or to the junction between the capacitor and the resistor.

19. An amplifier as claimed in any one of claims 7 to 18, in which the oscillator is arranged to operate on a steep portion of its resonance curve so as to provide a relatively large change in amplitude of the alternating signal when a coin passes t ; rou2h the field of the measuring coil.

20. An apparatus as claimed in any one of claims 7 to 19, in which the comparator circuit output is connected via an attenuator to the oscillator so that the correction st2nal produced at the comparator circuit when a coin passes through the field is increased by the ratio of the attenuator with respect to the attenuated correction signal sucplied to the oscillator required to main tain the amplitude of the alternating signal substantially constant.

21. An apparatus as claimed in any one of claims 7 to 20, in which there is pro vided a coin guide for coins to be checked, the coin guide comprising a vertical or oblique chute and the measuring coil comprising an annular coil arranged around the chute.

22. An apparatus as claimed in any one of claims 7 to 20, in which there is provided a coin guide for coins to be checked, the coin guide comprising a slide path and the measuring coil at a side of the slide path against which a coin to be checked is supported during its movement along the slide path.

23. An apparatus as claimed in claim 21 or 22, in which there is provided a mechanical sorting device for checking the dimensions of a coin to be checked and arranged lo guide coins whose dimensions are acceptable into the coin guide.

24. An apparatus for performing the method of claim 1, substantially as hereinbefore described with reference to Figure 1 or 2 or 3 or 4 or 5, to Figure 6 or 7 or 8, and to Figure 9 or 10 of the accompanyingdrawings.